Various types of interfaces between a rotary actuator and a linear controller have been devised. Rotary actuators are preferred for many applications due to their high reliability and relatively low cost. An interface may include a rising stem with a valve member at the lower end thereof, and the interface converts the rotation of the rotary actuator to raising and lowering the stem and thus moving the valve member on or off its seat.
While the rotary actuator may be relatively simple and reliable, the interface between the rotary actuator and the control device in many cases is not sufficiently rugged for field applications, including oilfield applications. Some interfaces are not suitable for corrosive environments which may accompany the application, while other actuators do not provide sufficient bearing support or weatherproofing for long term use.
A rotary actuator for raising and lowering a valve stem is disclosed in U.S. Pat. No. 6,007,047. U.S. Pat. Nos. 4,293,117 and 4,350,322 each disclose an actuator for a plug valve. U.S. Pat. No. 5,005,805 discloses a lift-turn actuator for a tapered plug valve, and U.S. Pat. No. 5,108,073 discloses an actuator for the reciprocation of a valve stem of a butterfly valve. U.S. Pat. No. 7,007,922 discloses a regulating device and actuator to convert linear movement to rotational movement.
A direct acting electrically operated actuator is disclosed in U.S. Pat. No. 6,971,628 which avoids the conversion of rotary motion to linear motion. U.S. Pat. No. 6,769,665 discloses an electric valve actuator with a failsafe device.
The disadvantages of the prior art are overcome by the present invention, an improved rotary actuator interface is hereinafter disclosed.